Documented cases of arsenic problems in groundwater related to
natural contamination (Smedley, Kinniburgh 2001).
Click on any of the annotated hotspots for details.
A map by Amini et al, Swiss Federal Institute of Aquatic Science
and Technology,
showing the modelled global probability of geogenic arsenic
contamination can be found here

by S. Sambu and R. Wilson

"It is an uncanny
thought that this lurking poison (arsenic) is everywhere about
us,
ready to gain unsuspected entrance to our bodies from the food
we eat,
the water we drink and the air we breathe" Karl Vogel, 1928.

Acute Effects

Arsenic has been used since 3000 BC. In the United Kingdom, for
example, it was used to extract iron from iron ore. It has long
been known that arsenic is acutely toxic. Anyone who drinks
arsenic in water at 60 parts per million (ppm) will soon die.
There are several toxicological summary references for acute
effects available on the web such as SCORECARD, ASTDR, USEPA and
LSUMC.

Beneficial Effects

Arsenic has been used for many years for medicinal purposes. It
used to be used as a cure for diseases such as syphilis and has
been shown to assist in curing some leukemias. It was taken as a
medicine in Fowler's Solution for well over a century. That
arsenic at low levels is safe seemed to be reinforced by animal
studies that seemed to show that arsenic is beneficial (to
animals) at low doses. Indeed, the fact that laboratory animals
could not be persuaded to develop cancer misled toxicologists
throughout the world and greatly contributed to the present
catastrophe. Others have written about other possible beneficial
effects at very low levels. It is important to note
that the beneficial effects are for different medical outcomes
(end points) than either the acute or chronic adverse effects
and that both beneficial and adverse effects can be observed
simultaneously (as is well known for alcohol ingestion). Another
detailed article about beneficial uses of arsenic can be
found here. Mineral hot
springs in the USA still advertise arsenic pools and their
users, including this webmaster, are convinced that the effects
are beneficial! (But arsenic penetrates the skin only slowly).

Chronic Adverse Effects

Chronic
effects of prolonged low level exposure have recently
showed up. Among various summaries we link to an information
site run by ASTDR.
Skin pigmentation, keratosis and
skin cancers were found by Tseng in Taiwan in 1966 among people
who drank from arsenic contaminated wells (but no effect was
seen below about 150 parts per billion (ppb), which might
therefore be a biological threshold) and a very high incidence
of lung, bladder and other cancers was found in Taiwan by Dr.
Chien-Jen Chen in 1986 and by Dr. Allan Smith and
collaborators in Chile in 1993. These convinced WHO to recommend
lowering the regulatory level from 50 ppb to 10 ppb for arsenic
in water. It appears that there are no data on humans to contest
the idea that prolonged exposure to low doses is dangerous.
Although arsenic was used medicinally in "Fowler's Solution" (1%
arsenite), prolonged use had led to these chronic skin effects.
This was observed as early as 1888 by Hutchinson. A follow up of
a number of English patients treated with Fowler's Solution has
been reported by Dr. Susan Evans in published literature, in a
report at the February 1998 conference in Dhaka and in a presidential
address by Susan Evans to the Liverpool Medical
Institute, which is available for download in PDF format. This
shows that the use of "Fowler's solution" (which is primarily
medicinal arsenic) in the UK is probably responsible for 5
bladder cancer cases among the patients among whom only 1.6 were
expected from natural causes. The arsenic dose was equivalent to
an average lifetime dose that would come from drinking water
with about 25 ppb of arsenic therein.

After several years of low level arsenic exposure, various skin
lesions appear. These are manifested by hyperpigmentation (dark
spots), hypopigmentation (white spots) and keratoses of the
hands and feet. After a dozen or so years skin cancers are
expected. Twenty or thirty years after exposure to 500 ppb of
arsenic, internal cancers (lung, kidney, liver and bladder)
appear among 10% of all exposed. Moreover, the dose-response
relationship for these internal cancers is consistent with being
linear with no threshold. Photographs of a number of victims of
this poisoning are available both from Bangladesh and
from Inner
Mongolia.

Although the most dramatic effect was the observation of
internal cancers in Taiwan, the most extensive epidemiological
studies have come from the work in Chile, in which Dr. Allan
Smith of UC Berkeley has been heavily involved. They find the
extraordinarily surprizing result that ingested arsenic in
Chile has produced lung cancer at a rate greater than that of
a heavy cigarette smoker! Recently, the group identified an
effect of arsenic exposure to children - who have developing
lungs -. Children exposed to arsenic have ten times the normal
lung cancer incidence.

The Effect of Diet

An important issue for coping with arsenic exposure is the
effect of diet. A general issue can be stated: there is
frequently more than one cause of a cancer or a lesion. For
example lung cancer can be caused by cigarette smoking or
asbestos or both together, in a synergistic way such that the
risks multiply (rather than add) when both are present. In the
USA it has been found that people who have a good diet of fresh
fruit and vegetables (5 servings per day) have half the risk of
many cancers, including lung cancers caused by cigarettes, as
those without a good diet. By analogy, one might expect that the
lung cancer risk from arsenic will be less among those with a
good diet. Anecdotal indications from Bangladesh suggests that a
good diet reduces skin lesions, and the effect
is seen in West Bengal, but
the effect is small and the authors recommend that effort is
better spent on obtaining pure water. Nonetheless
epidemiological studies to confirm this are highly desirable.
Khaliquzzaman and Khan have calculated the "Arsenic Exposure of
Bangladesh Population through Food Chain" using known amounts in
food, in an unpublished World
Bank report. The amount is less than from drinking
water but not much less.

There are several specific chemicals that have been suggested
that would either (I) help to prevent arsenic lesions by rapid
removal of arsenic from the body or (ii) help to cure arsenic
lesions. Encouragement of methylation of the arsenic probably
accelerates methylation, but the methylation has been suggested
as a cause of internal cancers. The specific chemical that has
come to the mind of many health experts is selenium. It was
noted in the 1930s that effects of excess selenium can be
counteracted by adding arsenic to the diet because As and Se
combine. Does the inverse take place? It is reported that areas
with high incidence of arsenical lesions have low selenium in
the water. Some victims have low selenium levels. Does adding
selenium to the diet really help, either to prevent the lesions
from forming (likely), or to treat them afterwards (less
likely)? We have, with help from others, compiled a list
of references and
a recent
paper on the subject. Professor
Zuberi of Rajshashi University has suggested
methionine to reduce the arsenic lesions. Dr. OGB Nambiar has
suggested that ferrous sulphate, after conversion to sulfide by
bacteria in the colon, absorbs arsenic and assists safe
excretion. The evidence for these remains indirect, and there
may be (as suggested above) competing adverse effects. Only good
epidemiology can tell and this is under way in several places.

Regulatory Limits for Continuous Exposure

The regulatory limits on arsenic exposure were set primarily to
be sure that these acute toxic effects were avoided. The first
regulatory limit of which the webmasters are aware was set as a
result of a public inquiry (subsequent to arsenic being found in
beer) of six members chaired by the physicist William Thompson,
first Lord Kelvin, in 1903. They recommended that sake of
liquids with more than 100 grains of arsenious oxide per gallon
(which works out at about 90 ppb of arsenic or 0.09 ug/l) This
was reduced two fold over the next century and until recently
the limit set by Bangladesh, the United Kingdom, and the United
States was 50 parts per billion (ppb). But the discovery that
there are adverse
effects of continuous chronic exposure led WHO to
lower their recommendation to 10 parts per billion (10 ppb). The
European Union (EU) plans to enforce a standard of 10 ppb by
2003. After a long travail, on October 31st 2001, the
administrator of US EPA confirmed a new standard for drinking
water of 10 ppb to be enforced by 2006. In Australia there does
not seem to be a specific regulatory level but there are work
rules for those working around mine tailings sites.

The US EPA has recently come out with an extensive review of
mechanisms of action of Dimethyl Arsenic (DMA) and
its possible mechanisms of action. They cannot rule out a linear
dose response at the lowest doses. It is effectively impossible
to reduce the content of arsenic in drinking water to a risk
level of one in a million lifetime risk calculated with a linear
dose-response relationship, a risk level and a calculational
procedure frequently used by the U.S. EPA. The present 10 ppb
standard is perhaps the first in which the U.S EPA explicitly
compared costs and benefits and used a value of $6.1 million per
calculated life saved. References to the extensive US national
discussion are available on the "countries" page
and in particular the section on travail.

The Worldwide Scope of the Catastrophe

Arsenic contamination has become a problem in many parts of the
world. At first as a result of leaching from mine tailings in
Australia, Canada, Japan,
Mexico, Thailand, United Kingdom, and the United
States, but now also from the arsenic in natural aquifers
now or recently used for water supply in Argentina, Bangladesh,
Cambodia, Chile , China, Ghana, Hungary, Inner
Mongolia, Mexico, Nepal, New Zealand, Philippines,
Taiwan, the United
States and Vietnam. Arsenic was also widely used as a
pesticide. 20,000 tons a year was imported into the USA, and
perhaps double that amount was used, to spray on crops in the
USA alone. No attention was paid to the ultimate fate of the
chemical, and in consequence arsenic
now appears in foodstuffs . (Papers
describing data in some of these countries are listed by
country in the list of useful references. ) It is
important to distinguish the problems in Bangladesh, West Bengal
and, to a lesser extent, Inner Mongolia, Chile, Nepal and
Vietnam, from the problems that have been found so far in the
rest of the world. These situations have in common that they are
an alluvial plain where arsenic has been brought down from the
surrounding hills for millennia. It seems that no one has looked
carefully at similar geological situations such as the Mekong
delta or the Irrawaddy delta. In most of the world exposures
above 50 parts per billion (50 ppb) are rare, and once observed,
can easily be avoided. But the sheer scale of the problems in
Bangladesh dwarfs the imagination. The catastrophe is much worse
than the well-known catastrophe of the Chernobyl nuclear power
plant accident, the Bhopal isothiocyanate leak or the Kuwait oil
fires. For 90% of the Bangladeshi communities, pure water is
still a long time away.

The World Bank made a study for SE Asia in the beginning of the
21st century which is available on the web:

"Arsenic Contamination of Groundwater in South
and East Asian Countries"

The situation in Bangladesh has received a lot of attention
because it is the most important. The new Bangladeshi government
has made the solution of the problem a priority as stated
clearly by Prime
Minister Begum Khaleda Zia as she opened the special
WHO workshop in Dhaka on January 14th -16th 2002. Feroze
Ahmed presented an excellent review of the situation at
that time. Participants made recommendations
to the government of Bangladesh (GoB). Another (2002)
review from the NGO forum is copied here from the NAISU website
in pdf. Professor
Chakriborti of Kolkata (Calcutta), a tireless and
enthusiastic worker in the field regularly issues his reports on
the Bangladesh situation, has a year 2001 report
on Bangladesh which we have also captured in a local
file.

Arsenic is plentiful in the ground. Yet it does not always
appear in the water supply. Scholars at the Cambridge University
Department of Geography have identified the following mechanisms
for arsenic entering the water which vary between locations.
Alkali-desorption, Geothermal, Reductive dissolution and
Sulphide oxidation. Although the worst arsenic catastrophe is in
Bangladesh, where 35 million people are exposed to levels above
the US EPA standard, the amount of arsenic in the soil is less
than in many other areas, including areas such as Massachusetts,
USA, where it does not, nonetheless, appear in unsafe quantities
in ground water. In most of these areas, such as the delta of
the Ganges and Irrawaddy, and the bend of the Yellow river,
arsenic has come down from the mountains over millennia,
attached itself to iron, forming iron pyrites, and been
deposited. Professor McArthur of UC London argues: "It becomes
increasingly clear that severe arsenic pollution of ground water
in most alluvial aquifers worldwide is driven by the
microbially-mediated metabolism of organic matter, with FeOOH
acting as the source of oxygen: the oxide is reduced during the
process and its sorbed arsenic is released to ground water.
Despite the widespread acceptance of this mechanism, much about
it remains obscure." One issue is whether the reduction takes
place at the surface before the water filters down to the
aquifer in the monsoon (as suggested by group (a) below) or
whether it is reduced in the aquifer itself.

Papers describing this mechanism include:

Two papers were presented by Charles Harvey et al.:
"Arsenic. Its Biogeochemistry and Transport in Groundwater,"
in "Biogeochemical Cycles of the Elements""Subsurface
geochemistry and arsenic mobility in Bangladesh"
"Response to Technical Comment on “Arsenic Mobility and
Groundwater Extraction in Bangladesh" and a brief report
in Science.
Most recently they suggest that reduction occurs in arsenic
ponds before water enters the aquifer.

An older idea was that water was being drained from the
aquifer, allowing oxidation. A recent paper describing arsenic
contamination in Perth, Australia - shows that there is one
location, in Perth where pyrite oxidation clearly WAS the source
of the As (although there is evidence that anaerobic release
from Fe oxyhydroxides is also taking place deeper in the
aquifer). But the ideas that pyrite oxidation is the problem in
Bangladesh whether caused by recent rapid
pumping that allowed for oxidation and release of
arsenic, or by the man-made change in river flow, such as
the barrage across
the Ganges are now considered to be untenable.

In the Americas, from Alaska in the north, through Crater Lake
in Oregon, Mono Lake and Searles Lake in California, volcanic
lakes in Nicaragua and Costa Rica, and on to the Andes, lie a
chain of volcanic activity that brings arsenic to the surface.
This mechanism of sulfate reduction in the arsenic-rich soda
lakes (Mono Lake and Searles Lake) of is being
studied in detail by Dr. Oremland and his group at
the US Geological Survey in Menlo Park. They attribute the
mechanism to bacteria, but of course different bacteria from
those responsible for the reduction of iron pyrites in SE Asia
and Bangladesh. Presumably this is the same mechanism as is
responsible for the arsenic pollution in the mountains of
Argentine and Chile where so much epidemiological studies have
been made.

Social Issues

Western experts from developed countries often regard the
arsenic pollution problem as a technical problem to be solved by
purely technical means. But that is naive. There are tremendous
social issues which control the ability of anyone to help. One
set of papers discussing was prepared by the Arsenic Policy
Support Unit in Bangladesh, (APSU) which is now defunct, but
these papers are copied
on this site.

Possible Solutions to the Problems

The first and most obvious necessity is to measure the
arsenic levels in any ground water that is intended for human
use. The next step is to purify
the water or, better still, provide an alternate
supply of pure water. The way in which this is done varies from
country to country. In SE ASIA, and Bangladesh in particular,
two facets of a solution seem to be agreed.

There is no one solution for all places and communities. It
is vital to involve the local community in the decision and
even more important in the follow up and maintenance.

The solution in any community and location must be based
upon the best possible scientific understanding. The webmaster
has attempted to summarize the possibilities in the remediation
page. Please add and correct. It is very important to
share data and experiences as set out in declarations from
seven arsenic conferences in Dhaka held by Dhaka Community
Hospital.

Contact Us

Please tell us what is missing from this
website, and send any useful material you know about to us
at wilson5@fas.harvard.edu .
If you wish to be informed of any updates, please send an e-mail
and say: "Please keep me informed!"